Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Fresh_Start on February 17, 2016, 08:56:28 pm
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The PT for my next build requires splicing both primary wires for 120 volts AC.
My first thought was to use a tag strip. Easy, cheap and the joints won't be subject to any mechanical movement after soldering. However, there would be at least 4 points where high voltage is exposed.
I could splice the leads and then use shrink wrap. If I did this, should I put all 3 wires together with the ends all pointing the same way and solder a pigtail, or should I put the 2 PT leads parallel and then join them in line with the wire going to the power cord? IOW power cord hot pointing toward two PT leads to form sort of a Y before soldering. This has the advantages of insulated joints and not using up precious real estate in a small chassis. OTOH the solder joints would be floating.
Then there are terminal blocks. I want a soldered connection, not a screw, but these offer protection from exposed high voltage. Can anyone point me toward an appropriate terminal strip for this application?
It's a bit embarrassing to ask such a basic build question, but this doesn't seem like a good place to experiment or compromise. These connections need to be rock solid and safe.
Thanks,
Chip
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Personally I use wire nuts. For more safety wrap them in el tape. Always wrap the tape in the direction that tightens the wire nut. This works for electricians and all kinds of household appliances, etc. The leads can be held in place with plastic zip ties.
Another option, instead of shrink wrap, is heat shrink boot insulation, which is more heavy duty. E.g.: http://www.alibaba.com/product-detail/Heat-shrinking-electrical-Insulation-breakout-boot_60216857261.html?spm=a2700.7724857.29.46.5nmsme (http://www.alibaba.com/product-detail/Heat-shrinking-electrical-Insulation-breakout-boot_60216857261.html?spm=a2700.7724857.29.46.5nmsme)
Also, I think tag strips & solder are fine. That's how the PT leads of my vintage Stromberg Carlson PA amps are wired, stock. (The filter caps are all exposed hi voltage anyway.) I would use solder & tags, rather than screw terminals.
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I remember watching a video about the lineman's splice. They use it on really high voltage connections. https://www.youtube.com/watch?v=BPrwUVEUPfc (https://www.youtube.com/watch?v=BPrwUVEUPfc) one of my fave channels just get a good shrink tube on it first, do it like that, soak it in solder and then cover it with shrink tube and heat to coverage, It is an extremely solid, clean and high quality joint. If you're splicing multiples, you can get a two strongly done like that, and then carefully wrap the other lines over that one with good contact before soldering and then cover with shrink tubing. Maybe I'm missing what you mean, though.
~Phil
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Thanks Phil - I'd forgotten about the linesman splice. Good method. It reinforces the concept of having a good mechanical Kong first, then soldering that joint. However, I need to have two wires from the PT joined together, then joined to the hot wire from the power cord.
Would it be OK to make a pigtail out of the two PT leads and then use the lineman's splice to connect the first two to the power cord lead?
Chip
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Either method (wirenut or similar; all wires enter from the same direction) or lineman's style makes a perfectly functioning splice if done in a workmanlike fashion. Which one I vote for depends upon how much space the wires and the big fat splice take up.
I like to slip a piece of jacketing from some coax cable over the soldered joint and enclosed all in shrink. I don't fully trust shrink-tube (only) for a HV splice. It gets thin as it gets stretched around a soldered joint. If you're using a wirenut, that's sufficient just as it is. I like to throw a tie-wrap (or two) around the wires going into the wirenut for strain relief. I kind of prefer the wirenut same-direction approach if it allows the wirenut to be tucked into some otherwise unused space. Also, for HV, I am most likely using heavyish wire so it might have some curl to it. In general, I don't use heatshrink at all---I just look for some coax jacketing that will fit tightly over the soldered joint, one-way-entry-prepped as if it was going into a wirenut, and hang off the end of the internal solder joint by 3/8" or so, empty. Just a tight-fitting tube held on by friction, but more abrasion resistant than heatshrink. I have soldered joints that have worked that way for 30 years. Belden 8451 (twinax #22 AWG w/foil shield) or 8422 (similar) is utterly perfect for insulating soldered joints between your lightweight hookup wire, though it may not slip over cloth-covered wire so nicely. Either way, "wirenut" or lineman's style. Comes right off should you need, stays put very well over the roughness of the solder joint. Free. If you are wiring a new studio, you'll have hundreds of 1 inch long little tubes and or 6" odd lengths of 8451 jacket and you fill up a pill bottle with those and just slip them over spliced solder joints on a temp basis and you're done.
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Thanks elevenTeen! That coax cable sheathing idea is excellent. Thicker and much stiffer to protect the joint.
Chip
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As far as three in one, I'd do the lineman's first, then wrap the third around the other two tightly, almost like the first lineman's, but only half. Then the solder would make that one hold really well after you ensure the strong mechanical connection
Phil
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+1 to eleventeen. I have not had shrink tube say put. My concern is how to reliably keep the lineman's splice insulated. Another option mentioned is the crimp on butt connection. Must be correctly sized to your wire. They come insulated & uninsulated. I always have problems with the crimp, so I crimp & solder.
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In the late 70's I hopped up my SF PR to dual 6L6 with Altec 417-8H speaker. Very tight fit. The Altec speaker is a very deep spider type and I had to move the (bigger, standup) OT to the preamp end of the amp. I did not want to run OT wires past the preamp (gee, even 40 years ago I knew this) inside the chassis so I ran them over the top of the chassis in a bundle. So I have the biggest B+ in the amp running through there---3 times, given CT & 2 plates. All those splices are double-salvaged coax jacketed with a couple of nylon "P" style cable clamps and they've been there for nearing 40 years with zero problems.
The whole key with splicing is to not use any one thing for more than one purpose. The insulation should not be the mechanical and vice versa (eg; use tie-wraps entering the wirenut) Shrink tubing has no "pull-together" power. It can shrink over a projection and stay in place....but I still don't trust it.
CAT5 cable which you always end up with tens of feet of scrap, is also useful jacketing for LV applications.
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Check out NEETS (http://jacquesricher.com/NEETS/). Download Module 4, and open it to Chapter 2.
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Check out NEETS (http://jacquesricher.com/NEETS/). Download Module 4, and open it to Chapter 2.
Thank you very much. I had forgotten about the NEETS training manual, and I learn new things every time I review it.
You guys are great!
Chip
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NEETS says to use el tape to insulate a linesman splice. Not appealing to me.
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NEETS says to use el tape to insulate a linesman splice. Not appealing to me.
I agree, but that would be perfectly acceptable in a location/use case where it never moves. Like in a house or in a wall mounted cabinet.
In a guitar amp that moves constantly and has heavy abuse, you're 100% right, its a BAAAD idea, but imho so are wire nuts, they can come loose too. Physical connections should be soldered, screwed down, etc.
I need to fix a few issues like that in my current build still.
~Phil
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NEETS says to use el tape to insulate a linesman splice. Not appealing to me.
I mainly linked to it because it shows several methods of splicing wire.
As for the tape... use what you think is best for insulation/durability. I think the electric tape info was more of an aside in that module. I've seen rubber tape being used to build up bulk as a strain-relief in a large cable before shielding & cloth covering is wound over. I also don't see many folks bothering to pick up the wire-lacing they present in that module, either. :icon_biggrin:
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> should I put all 3 wires together with the ends all pointing the same way and solder a pigtail, or should I put the 2 PT leads parallel and then join them in line with the wire going to the power cord?
Yes.
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I have not found a power splice system I am totally happy with.
Too many wire-nut failures (especially on fine-strand wire). Tape doesn't last forever, and there is a real knack needed to make it last a while. I do like shrink-tube, even on BIG wire (100 Amp), but I double-layer. Cheap shrink is as useful as pre-used condoms (there's a story...).
Solder is no longer used in house wire because when you have a BIG short it spews molten metal. Perhaps not an issue behind 6 feet of lamp-cord, or even a common PC/IEC cord. But also most solderers can't really be trusted (I see too much on DIY forums).
Between a devil and a deep blue sea, I'm favoring euro-style terminal blocks:
(http://www.mouser.com/images/altech/images/eurostrips.JPG)
Mouser Part #: 845-HE1WPR/12
I am finding screw-clamp terminations very reliable *and* inspectable. The nylon body is safe for 230V (300V) work. The block can (and should!) be screwed to chassis for mechanical location. If you ever move to France you can re-rig the windings on a whim. You do need to keep a strong narrow screwdriver at hand.
Where space is less tight, I am liking DIN Rail terminations; but these need 2"-4" height and width (length can be as low as 6mm per circuit, good for many-wire mangles).
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Reusing vintage transformers can be a pain. The insulation was not at its best once I removed the transformer from the chassis, especially at the bell.
(http://i406.photobucket.com/albums/pp142/printer2_photo/guitar%20amp/5E3BFPT.jpg)
Did the best that I could under the circumstances.
(http://i406.photobucket.com/albums/pp142/printer2_photo/guitar%20amp/5E3transformerrepaired.jpg)
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PRR - I'm never moving to France but really like those Eurotrash strips. Thanks!
Chip
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I've lived in France, it's a great place :) But home is where you are I guess ;) BTW that Transistor cleanup looks amazing printer2!
~Phil
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NEETS says to use el tape to insulate a linesman splice. Not appealing to me.
I mainly linked to it because it shows several methods of splicing wire.
As for the tape... use what you think is best for insulation/durability. I think the electric tape info was more of an aside in that module. I've seen rubber tape being used to build up bulk as a strain-relief in a large cable before shielding & cloth covering is wound over. I also don't see many folks bothering to pick up the wire-lacing they present in that module, either. :icon_biggrin:
Don't get me wrong. I'm not criticizing NEETS. That is all great info! Also learned I've been knife-stripping wires incorrectly & will try the NEETS "pencil sharpening" method.
Euro tag strips are appealing. But over time I wonder about oxidation and galvanic corrosion between the wire leads & screw terminals. A coating of solder helps prevent that, and tag strips are less expensive.
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> I wonder about oxidation and galvanic corrosion between the wire leads & screw terminals
Yes; but pressure connection is old/mature technology.
A good pressure connection is essentially gas-tight at the pressure point. A couple decades later, the wire is still bright and shiny under the clamp.
And the contact materials are designed for the metals involved. (Copper easy, Al-rated may cost more.)
Note that all your house outlets are (I hope) pressure connectors, screw terminals. This includes high current connections in outdoor service boxes; screws may be 1/4" diameter.
There ARE bad pressure connectors. They still make the wall-outlets where you just poke #14 into holes in the back. A light spring makes contact. The pressure is too light to be gas-tight. This was marketed long ago, cost little so was widely used, and has made trouble. A small sector of the electrical industry (manufactured housing) resists banning it. But any back-stab I find, I change over to side-screw. (Don't confuse backstab with "good" outlets- there is a hole, but you clamp it with the screw.)
I would hope for little galvanic action in an amplifier. However the standard connector for down-the-well pumps is a pressure connector, not too unlike the things inside the Euro-Terminals above. This is then put inside a goo-packed sleeve to keep the well water out, of course; but such things can seep. This does not *seem* to be a prime cause of well trouble.
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Good to know, thanks!